petrographer 
petrographer (pet-rog'ra-fer), n. [< petrogra- 
plt-y + -tr 1 .] One who is versed in petrogra- 
phy, or the study of rocks. 
petrographic (pet-ro-graf'ik), a. [= F. p6tro- 
i/niphitjuc; as petrograpli-y + -if.~\ Of or per- 
taining to petrography. 
petrographical (pet-ro-graf'i-kal), a. [< pet- 
rograpMe + -al.J Same as petrographic. fet- 
ro'graplilcal microscope. See microscope. 
petrographically (pet-ro-graf ' i-kal-i), adv. As 
regards petrography; as regards mineralogi- 
cal and chemical constitution and structure: 
as, two kinds of gneisspetrograpMeally distinct. 
petrography (pet-rog'ra-fi), n. [= F. petro- 
graphie, < Gr. irerpa, a rock, nerpof, a stone, + 
-ypa<t>ia, < jpd<t>eiv, write.] If. The art of writing 
or inscribing on stone. 2. The study of rocks ; 
lithology; petrology. The investigation of the miner- 
als of which rocks are made up is called lithology, which in- 
cludes not only the determination of the mineral constitu- 
ents of a rock, but also the study of the changes which these 
constituent minerals have undergone, either during the 
consolidation of the rock or at a subsequent period, in the 
course of those changes which are denominated metamor- 
phic (see metamorphiitn) changes often complicated 
and difficult to decipher. While in some rocks the con- 
stituents are crystallized in large and distinctly formed 
individuals, so that each species can be separated and an- 
alyzed by itself without difficulty, this is ordinarily not 
the case. Hence by the methods formerly pursued it was 
often extremely difficult, if not impossible, to make out 
clearly of what species the rock was composed. At the 
present time the method of examination of a rock consists 
in cutting from it one or more sections sufficiently thin to 
be nearly transparent ; these are examined with the mi- 
croscope, with and without the use of polarized light ; and 
the optical and crystallographic appearances presented 
are generally sufficient to give not only a correct idea of 
the nature of the minerals, but also of the changes which 
they have undergone through various stages of metamor- 
phism. Assistance is also afforded by the method of sepa- 
ration in which gravity -solutions are employed. (See grav- 
ity-solution.') While most geologists writing in English use 
the terms lithology, petrology, and petrography as nearly sy- 
nonymous, others desire to limit the meaning of the first 
of these to the indoor or laboratory study of rocks, and 
would define petrography as including their investigation 
both indoors and in the field. 
Petrography I define as that branch of science which em- 
braces both lithology and petrology. It includes every- 
thing that pertains to the origin, formation, occurrence, 
alteration, history, relations, structure, and classification 
of rocks as such. It is the essential union of field and lab- 
oratory study. M. E. Wadxworth, Lithological Studies, p. 2. 
petrohyoid (pet-ro-hl'oid), a. and n. [< petro(us) 
+ hyoid.'] I. a. Of or pertaining to the hyoid 
bone and a petrous part of the skull: noting a 
muscle of some batrachians Petrohyoid mus- 
cle, a series of small muscular slips lying immediately be- 
neath the omohyoid, and passing between the hyoid and 
hinder region of the skull of some batrachians. Huxley 
mid Martin, Elementary Biology, p. 50. 
II. . The petrohyoid muscle. 
petrolt (pe-trol' or pet'rol), . [< F. petrole, < 
ML. petroleum : see petroleum.] Same as petro- 
leum. 
Petrol or petroleum is a liquid bitumen, black, floating 
on the water of springs. Woodward. 
petrolatum (pet-ro-la'tum), n. [NL., < petro- 
leum, q. v.l A soft unctuous substance, con- 
sisting mainly of hydrocarbons of the paraffin 
series, obtained from residues left after the dis- 
tillation of lighter oils from crude petroleum, 
or deposited from crude petroleum on standing. 
When purified and deodorized, it forms a salvy neutral 
mass, yellow or reddish in color, odorless, tasteless, and 
somewhat fluorescent. It is used as a basis for ointments 
and as a protective dressing. Also called vaseline and cos- 
moline. 
petrolene (pet'ro-len), . [= F. petrolene; as 
petrol, petrol(eum), + -ewe.] A liquid hydrocar- 
bon mixture obtained from petroleum. 
petroleum (pe-tro'le-um), n. [=F. petrole =Sp. 
petroleo Pg. petroleo = It.petrolio = D . G. Dan. 
Sw. petroleum (MD. peterolie), < ML. petroleum 
(&lsopetreleum,petrelseon, < MGr. NGr. vcTpehai- 
ov), rock-oil,< Ij.petra (< Gr. ireTpa), rock,+ ole- 
m(<Gr. e%uov),oil: seeoil. AMLi.aAj.petrole- 
tis, pertaining to rocks (neut. petrole urn, or oleum 
petroleum, rock-oil), is given.] An oily sub- 
stance of great economical importance, espe- 
cially as a source of light, occurring naturally 
oozing from crevices in rocks, or floating on the 
surface of water, and also obtained in very large 
quantity in various parts of the world by boring 
into the rock ; rock-oil. Petroleum was known to the 
Persians, Greeks, and Romans under the name of naphtha; 
the less liquid varieties were called ao-cJmATos by the Greeks, 
and bitumen was with the Romans a generic name for all the 
naturally occurring hydrocarbons which are now included 
under the names of asphaltum, maltha, and petroleum. The 
last name was not in use in classic times. The existence of 
petroleum in Pennsylvania and New York has been known 
from almost the earliest time of the settlement of those 
States by Europeans, but it was not until 1859, when oil 
was obtained by boring at Titusville on Oil Creek, a branch 
of the Allegheny River, that it began to be of commercial 
Importance. At the present tune the production of crude 
4428 
petroleum reaches an amount nearly equal to thirty mil- 
lions of barrels a year, and the value of the exports of this 
article in various forms amounts to almost 50,OUO,000 a 
year, nearly all the material exported being furnished by 
the oil-fields of Pennsylvania and western New York. The 
crude oil undergoes refining, and is put upon the market 
in various forms (see kerosem, naphtha, rhiyolene. etc.), 
but much the largest part of this product has the form 
of an oil suitable for burning in lamps in all parts of the 
world. The only other oil-producing region in the world 
at all comparing with that of Pennsylvania and New York 
is at and near Baku, on the Caspian, where the existence 
of oil has been known from time immemorial, but where 
its commercial importance has only recently been realized. 
The exported petroleums of the United States are chiefly 
from rocks of Devonian age ; those of Baku occur in the 
Tertiary. An important part of the transportation of the 
crude material in the United States is effected by pipes 
laid beneath the surface, through which the oil is forced. 
See pipe-line. Also called coal-mi, earth oil. 
The Wardrobe Account, 21-23 Edw. III., 38/2, the fol- 
lowing entry : " Delivered to the King in his chamber at 
Calais : 8 Ibs. petroleum." If. and Q., 7th ser., V. 248. 
petroleum-car (pe-tro'le-um-kar), n. A rail- 
road-car carrying a tank or tanks, especially 
designed for the transportation of petroleum 
in bulk. 
petroleum-ether (pe-tro'le-um-e"ther), n. 
Same as naphtha. 
petroleum-furnace (pe-tro'le-um-f6r"nas), n. 
A steam-boiler or other furnace for burning 
petroleum, which is admitted in jets or in the 
form of a spray of petroleum mingled with air 
or with a steam-jet; a hydrocarbon-furnace. 
E. H. Knight. 
petroleum-still (pe-tro'le-um-stil), n. A still 
for separating the hydrocarbon products from 
Petromyzontidse 
petrology (pet-rol'o-ji), n. [< Gr. irerpa, rock, 
TrtT/iof, a stone, + -Aoyia, < 'Atyeiv, speak: see 
-<>loyy.~\ The study of rocks from the point of 
view of their minerulogical composition; lithol- 
ogy ; petrography. By some this term is used 
in a more limited sense. See the quotation, 
and also petrography. 
Lithology describes the results which would be arrived 
at by a man who sat indoors in his laboratory and examined 
small hand specimens of different kinds of rocks brought 
to him. Petrology tells us what additional information we 
k'ain when we go out of doors and examine large masses of 
rocks in the fields. A. H. Green, Phys. Geol., p. 9. 
petromastoid (pet-ro-mas'toid), a. and n. [< 
petro(ua) + mastoid.~] I. a. Of or pertaining to 
the petrous and mastoid parts of the temporal 
bone: as, petromastoid cells ; the petromastoid 
bone. 
II. . The petromastoid bone. In man at birth 
the petromastoid is a distinct bone, consisting chiefly of 
petrosal elements from which mastoid parts are as yet 
scarcely developed. It soon becomes confluent with oth- 
er parts of the compound temporal bone, leaving traces 
of its original separation in the Glaserian fissure and the 
canal of Huguier on the outer side of the bone, and the 
Eustachian tube and tensor tympani canal on the other 
side. 
Petromys (pet'ro-mis), n. [NL. (Sir A. Smith, 
1831), < Gr. mrp'a, rock, + //if, mouse.] A re- 
markable outlying genus of rodents of the fam- 
Petromys typictis. 
ily Octodontidie, found in Africa; rock-rats. It 
is one of the only three Ethiopian genera of 
this characteristically American family. 
Petromyzon (pet-ro-mi'zon), . [NL.,< Gr. m- 
Ty>a,rock, frerpof, a stone, + //!'<ji> (//i>(ovr-),ppr. of 
[tv&iv, suck: see myzont. Cf.petromyzont.} 1. 
A genus of myzouts or lampreys, giving name 
to the family I'etromyzontidif. It formerly in- 
cluded all the lampreys and other myzonts, but has by later 
ff 
Petroleum-still. 
a. retort; a', beak of retort, through which vaporspass: 6, charging- 
pipe ; f, column composed of compartments f 1 , c y , etc. (The com- 
partments are filled to a definite height with the same kind of liquid 
as that to be distilled through the pipe d, having a valve for each com- 
partment. The same pipe is also used for drawing off this liquid.) 
e, worm placed in a water-tank, connected by pipe^to the column 
c, and by the pipe g to a gasometer k ; h, h', auxiliary worms con- 
nected with t ; J, pipe for return of liquid to the retort when desired ; 
/, I, running-pans receiving liquid from h. h', etc. ; tn, main run- 
ning-pan. Heat is applied by furnaces at the bottom of a. The va- 
pors pass through a into c. The heavier products are condensed by 
the liquid in the compartments c 1, c z , etc. Lighter vapors pass into 
the worm f, and are there condensed and run down into h and h' for 
further cooling. The gasometer 6 collects any uncondensed vapors. 
crude petroleum in the order of their volatility. 
E. H. Knight. 
p6troleur (pa-tro-ler'), [F-, < petrole, pe- 
troleum : see petroleum."} An incendiary ; spe- 
cifically, one of those adherents of the Com- 
mune who set fire to the public buildings of 
Paris, with the aid of petroleum, on the entry 
of the national troops in May, 1871. 
p6troleuse (pa-tro-lez'), n. [F., fern, of feiro- 
leur, q. v.] A female incendiary. Seepe'troleur. 
petroliferous (pet-ro-lif 'e-rus), a. [* ML. pe- 
troleum, petroleum, + L. ferre = E. Sear 1 .] 
Abounding in petroleum ; productive of petro- 
leum; containing or yielding petroleum: as, 
petroliferous strata. Amer. Jour. Set., VII. 561. 
petrolin, petroline (pet'ro-lin), n. [< petrol, 
petrol(eum), + -in 2 , -ine%.~\ A solid substance 
consisting of a mixture of hydrocarbons, ob- 
tained by distilling the petroleum of Rangoon : 
analogous to paraffin. 
petrolist (pet'ro-list), n. [<. petrol + -ist.~\ An 
incendiary. See petroleur. 
petrolize (pefro-flz), v. t. ; pret. and pp. petro- 
lized, ppr. petrolizing. [< petrol + -ize.] To 
cause to resemble petroleum ; confer the char- 
acter or properties of petroleum upon. Ure. 
petrological (pet-ro-loj'i-kal), a. [< petrolog-y 
+ -ic-nr] Of or pertaining to petrology. Nature. 
petrologically (pet-ro-loj'i-kal-i), adv. As re- 
gards petrology or petrological investigation or 
conditions. 
petrologist (pet-rol'o-jist), n. [< petrolog-y + 
-ist.~\ One who is skilled in petrology. 
Skull of Lamprey (Petromyxon 
A, side view : B, top view : a, ethmovomerine plate ; b, olfactory 
capsule ; c, auditory capsule ; d, neural arches of spinal column ; f, 
palatopterygoid ; f, (probably) metapterygoid, or superior quadrate, 
and , inferior quadrate part of the subocular arch ; ft. stylohyal 
process; t, lingual cartilage ; *, infe: 
of cranium; m, branchial skeleton ; i 
, and /, lateral, prolongation 
3, accessory labial cartilages. 
writers been restricted to the northern lampreys, and es- 
pecially those of the sea. See Petromyzontidx, and cuts 
under basket, lamprey, and Margipobranchii. 
2. [1. c.] Any member of this genus, as a lam- 
prey. 
petromyzont (pet-ro-mi'zont), n. [< NL. Pei- 
romyzon(t-).~] A lamprey. 
Petromyzontia (pefro-mi-zon'shi-a), n. pi. 
[NL., neut. pi. of Petromyzon.~\ The lampreys 
as a class of cyelostomous craniate vertebrates : 
distinguished from Myxinoidea or hags. Also 
called Hyperoartia. 
Petromyzontidae (pet"r6-mi-zon'ti-de), n. pi. 
[NL., < Petromyzon(t-) + -idse.~\ A family of 
cyelostomous or marsipobranchiate fishes ; the 
lampreys. They are elongated eel-like animals, whose 
adults have a complete circular suctorial mouth iirnn-d 
with an upper and lower jaw-like cartila^i 1 , tfL'th on the 
tongue and on the oral disk, seven branchial apertures on 
